1. Field of the Invention
The present invention relates to the field of controlled electric power transfer of the type designed, for example, to control or regulate the supply of alternating current electric power to a load in response to a device sensing voltage, current, temperature, motor speed, humidity, or another similar characteristic or quantity.
The present invention relates more particularly to a form of electric power control achieved by means of a variable reactance having a control coil selectively shortcircuited to cause the loading of a core and to decrease the reactance of another winding about that core. This form of power control has a number of advantages. Large amounts of power can be controlled using controllable short-circuiting switches, such as SCR's and other thyristors, of lesser power handling capacity. Precise control can be achieved, and the power used in controlling is small. In addition, capacitative switching effects are masked.
2. Description of the Prior Art
Various known arrangements achieve power regulation by periodically loading a control core with a selectively short-circuited control coil. Examples of such arrangements are shown in the following U.S. Pat. Nos.: 3,184,675 (Macklem); 3,199,018 (Macklem); 3,103,619 (DuVall); 3,573,605 (Hart); 3,739,257 (Hunter); 3,295,053 (Perrius); 2,725,508; 2,497,218; 3,065,399; 2,767,364; and 3,182,249.
Although the arrangements described in the foregoing patents are able to provide power control, they have not been fully satisfactory. Considerable amounts of magnetic core material and copper coil material are needed to provide sufficient reactance for control in the known arrangements. Moreover, power dissipation in the short-circuited control coil often is at a level high enough to create design problems. Finally, such known control arrangements often do not provide good efficiency in terms of power transfer.